U.S. patent application number 15/267236 was filed with the patent office on 2017-01-05 for load drive circuit.
This patent application is currently assigned to Yazaki Corporation. The applicant listed for this patent is Yazaki Corporation. Invention is credited to Yoshinori Ikuta, Yoshihide Nakamura, Shuuji Satake, Yasuyuki Shigezane, Keisuke Ueta.
Application Number | 20170005653 15/267236 |
Document ID | / |
Family ID | 54324189 |
Filed Date | 2017-01-05 |
United States Patent
Application |
20170005653 |
Kind Code |
A1 |
Ueta; Keisuke ; et
al. |
January 5, 2017 |
Load Drive Circuit
Abstract
A load drive circuit shuts off power supply to a load when a
semiconductor relay is off. The load drive circuit includes: the
semiconductor relay which is turned off when a predetermined
operation voltage cannot be secured; a low-voltage detection
circuit which detects that the operation voltage is a predetermined
value or less; a negative-voltage generation circuit which
generates a negative voltage; and a switch unit which is turned on
and connects between the negative-voltage generation circuit and a
ground terminal of the semiconductor relay, in a case where the
low-voltage detection circuit detects that the operation voltage is
the predetermined value or less.
Inventors: |
Ueta; Keisuke; (Susono-shi,
JP) ; Nakamura; Yoshihide; (Susono-shi, JP) ;
Ikuta; Yoshinori; (Susono-shi, JP) ; Shigezane;
Yasuyuki; (Susono-shi, JP) ; Satake; Shuuji;
(Susono-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Yazaki Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
Yazaki Corporation
Tokyo
JP
|
Family ID: |
54324189 |
Appl. No.: |
15/267236 |
Filed: |
September 16, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2015/061914 |
Apr 17, 2015 |
|
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|
15267236 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02J 2007/0067 20130101;
H03K 17/22 20130101; H03K 17/30 20130101; H02J 7/0029 20130101;
H02J 7/0063 20130101; H02J 7/00306 20200101 |
International
Class: |
H03K 17/30 20060101
H03K017/30 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 18, 2014 |
JP |
2014-086506 |
Claims
1. A load drive circuit that shuts off power supply to a load when
a semiconductor relay is off, the load drive circuit comprising:
the semiconductor relay which is turned off when a predetermined
operation voltage cannot be secured; a low-voltage detection
circuit which detects that the operation voltage is a predetermined
value or less; a negative-voltage generation circuit which
generates a negative voltage; and a switch unit which is turned on
and connects between the negative-voltage generation circuit and a
ground terminal of the semiconductor relay, in a case where the
low-voltage detection circuit detects that the operation voltage is
the predetermined value or less.
2. The load drive circuit according to claim 1, wherein the
negative-voltage generation circuit generates the negative voltage
in a case of receiving a signal representing necessity of driving a
low-voltage drive load, and inhibits generation of the negative
voltage in a case of not receiving the signal, the low-voltage
drive load being a load which is determined in advance to be driven
even in a case where the operation voltage drops and hence the
predetermined operation voltage for the semiconductor relay cannot
be secured.
3. The load drive circuit according to claim 1, further comprising:
a control unit which outputs a ground switch ON signal in a time
period where the operation voltage is expected to be the
predetermined value or less, wherein the switch unit is turned on
and connects between the negative-voltage generation circuit and
the ground terminal of the semiconductor relay when the ground
switch ON signal is outputted from the control unit.
4. The load drive circuit according to claim 1, further comprising:
a control unit which outputs an ON/OFF signal for the semiconductor
relay; a connection line which connects an input terminal of the
semiconductor relay to which a signal according to the ON/OFF
signal is inputted and the ground terminal; and a voltage
conversion circuit which prevents, in a case where the control unit
outputs the OFF signal for the semiconductor relay, the
semiconductor relay being turned on by the negative voltage applied
to the ground terminal of the semiconductor relay from the
negative-voltage generation circuit.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of PCT application No.
PCT/JP15/061914, which was filed on Apr. 17, 2015 based on Japanese
Patent Application (No. 2014-086506) filed on Apr. 18, 2014, the
contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a load drive circuit.
[0004] 2. Description of the Related Art
[0005] In a power supply box (hereinafter referred to as unit) for
distributing electric power from a power supply in a vehicle,
utilization of semiconductors is expanding so as to cope with
requirement for weight reduction and power saving. Further in order
to promote miniaturization, utilization of a configuration
combining a conventional printer driver and an MOSFET (or other
device) is expanding, or utilization of an IPD (Intelligent Power
Device) as a device integrating a driver and a control circuit
having a protection function is expanding. An example of the IPD is
disclosed in below-described Patent Document 1. These devices
mostly contain a low-voltage shut-off function for preventing
overheat caused by increase of an on-resistance upon voltage
drop.
PRIOR ART DOCUMENT
Patent Document
[0006] Patent Document 1 is JP-A-2011-55333.
SUMMARY OF THE INVENTION
[0007] As a starter flows a large current, a terminal voltage of a
battery drops due to an internal resistance of the battery. In this
manner, the vehicle causes a phenomenon that the voltage drops
temporarily upon starting an engine (in particular, during
cranking). The vehicle contains loads required to be operated even
during cranking at which the voltage drops temporarily. The
low-voltage shut-off function is required to be avoided in order to
operate these loads also during cranking. In order to avoid the
low-voltage shut-off function, for example, it is considered to
provide an auxiliary battery for assisting supply of power upon
starting the engine or to provide a power system not relating to
the engine start. However, in these cases, the power supply system
is required to be changed entirely.
[0008] Further it is considered to mount a DC/DC converter for
stabilizing the voltage but, in this case, large-sized components
are required disadvantageously since a supply current is large.
[0009] Incidentally the temporal voltage drop also occurs during no
idling, for example, as well as during the cranking. Thus the
aforesaid problem commonly arises upon the voltage drop occurring
at other timing as well as the voltage drop at the cranking.
[0010] The present invention aims to solve such the problems and an
object of the present invention is to provide a load drive circuit
which can drive a load by avoiding a low-voltage shut-off function
during voltage drop, while suppressing the necessary number of
large sized components without requiring entire change of a power
supply system.
[0011] According to the present invention, there is provided a load
drive circuit including a semiconductor relay which is turned off
when a predetermined operation voltage cannot be secured, the load
drive circuit shutting off power supply to a load when the
semiconductor relay is off, the load drive circuit including: a
low-voltage detection circuit which detects that the operation
voltage is a predetermined value or less; a negative-voltage
generation circuit which generates a negative voltage; and a switch
unit which is turned on and connects between the negative-voltage
generation circuit and a ground terminal of the semiconductor
relay, in a case where the low-voltage detection circuit detects
that the operation voltage is the predetermined value or less.
[0012] According to the load drive circuit of the present
invention, when the operation voltage such as a voltage from a
battery is detected to be the predetermined value or less, as the
switch unit is turned on and connects between the negative-voltage
generation circuit and the ground terminal of the semiconductor
relay, a voltage of the ground terminal of semiconductor relay
becomes the negative voltage generated from the negative-voltage
generation circuit. Thus as the ground terminal is at the negative
voltage even when the voltage from the battery drops, the operation
voltage of the semiconductor relay can be secured and hence the
low-voltage shut-off function can be avoided. Further as the
low-voltage shut-off function can be avoided in the aforesaid
manner, it is not necessary to provide an auxiliary battery or a
power system not relating to the engine start, etc. or to mount a
DC/DC converter. Consequently the load can be driven by avoiding
the low-voltage shut-off function during the voltage drop, while
suppressing the necessary number of large sized components without
requiring entire change of a power supply system.
[0013] According to the load drive circuit of the present
invention, preferably, the negative-voltage generation circuit
generates the negative voltage in a case of receiving a signal
representing necessity of driving a low-voltage drive load, and
inhibits generation of the negative voltage in a case of not
receiving the signal, the low-voltage drive load being a load which
is determined in advance to be driven even in a case where the
operation voltage drops and hence the predetermined operation
voltage for the semiconductor relay cannot be secured.
[0014] According to the load drive circuit, the negative voltage is
generated when the signal representing necessity of driving the
low-voltage drive load is received, and the generation of the
negative voltage is inhibited when this signal is not received.
Thus when the low-voltage drive load is not required to be driven,
as the negative voltage is not generated, power consumption can be
suppressed.
[0015] According to the present invention, preferably, the load
drive circuit further includes a control unit which outputs a
ground switch ON signal in a time period where the operation
voltage is expected to be the predetermined value or less, wherein
the switch unit is turned on and connects between the
negative-voltage generation circuit and the ground terminal of the
semiconductor relay when the ground switch ON signal is outputted
from the control unit.
[0016] According to the load drive circuit, in the time period
where the operation voltage from the battery or the like is
expected to drop, the ground switch ON signal is outputted, thereby
causing the switch unit to connect between the negative-voltage
generation circuit and the ground terminal of the semiconductor
relay. Thus, for example, in a case where the voltage from the
battery is the predetermined value or less, even if the switch unit
is not turned on in response to the output from the low-voltage
detection circuit due to a failure of the low-voltage detection
circuit or the like, a voltage of the ground terminal becomes the
negative voltage in the time period where the voltage from the
battery is expected be the predetermined value or less.
Consequently as the operation voltage of the semiconductor relay
can be secured, the low-voltage shut-off function can be
avoided.
[0017] According to the present invention, preferably, the load
drive circuit further includes: a control unit which outputs an
ON/OFF signal for the semiconductor relay; a connection line which
connects an input terminal of the semiconductor relay to which a
signal according to the ON/OFF signal is inputted and the ground
terminal; and a voltage conversion circuit which prevents, in a
case where the control unit outputs the OFF signal for the
semiconductor relay, the semiconductor relay being turned on by the
negative voltage applied to the ground terminal of the
semiconductor relay from the negative-voltage generation
circuit.
[0018] According to the load drive circuit, in order to prevent the
semiconductor relay being turned on by the negative voltage applied
to the ground terminal of the semiconductor relay in the case of
outputting the OFF signal with respect to the semiconductor relay,
the voltage conversion circuit is provided. Accordingly the
semiconductor relay can be prevented being erroneously turned on
due to a fact that, for example, the input terminal of the
semiconductor relay is at 0V and the ground terminal is at the
negative voltage.
[0019] According to the load drive circuit of the present
invention, the load drive circuit can be provided which can drive a
load by avoiding a low-voltage shut-off function during voltage
drop, while suppressing the necessary number of large sized
components without requiring entire change of a power supply
system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a circuit diagram schematically illustrating a
load drive circuit according to an embodiment of the present
invention.
[0021] FIG. 2 is a circuit diagram illustrating details of a
voltage conversion circuit of the load drive circuit according to
the embodiment.
[0022] FIG. 3 is a detailed circuit diagram illustrating a main
portion of the load drive circuit according to the embodiment.
[0023] FIG. 4 is a timing chart illustrating an operation of the
load drive circuit according to the embodiment.
[0024] FIG. 5 is a circuit diagram illustrating a modified example
of the load drive circuit according to the embodiment.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0025] Although explanation is made as to a preferred embodiment
according to the present invention, the present invention is not
limited to the embodiment explained below but may be changed
suitably within a range not departing from the gist of the present
invention.
[0026] FIG. 1 is a circuit diagram schematically illustrating a
load drive circuit according to an embodiment of the present
invention. A load drive circuit 1 shown in FIG. 1 is mounted in a
vehicle and constituted as a unit provided between a battery B and
loads L. This circuit includes a power supply 10, a control unit 20
and plural IPDs (semiconductor relays) 30.
[0027] The power supply 10 is applied with a voltage from the
battery B and generates a prescribed voltage (for example, 5V). For
example, a power supply IC is used as this power supply. The
control unit 20 is constituted of a microcomputer, for example, and
outputs an ON/OFF signal to each of the plural IPDs 30. The control
unit 20 is applied with the voltage from the power supply 10 and
receives, upon turning-on of an ignition switch (or a starter
switch, a headlight switch), a signal representing this
turning-on.
[0028] Each of the plural IPDs 30 is the semiconductor relay
disposed between the battery B and corresponding one of the plural
loads L, and shuts off power supply to the corresponding load upon
turning-off of this IPD. In FIG. 1, illustration of connection
lines from the battery B to the loads L is omitted.
[0029] Each of the plural IPDs 30 has a low-voltage shut-off
function for turning itself off when the voltage from the battery B
temporarily drops and cannot secure a predetermined operation
voltage. This low-voltage shut-off function acts to prevent
overheat caused by increase of an on-resistance upon the voltage
drop. At least one IPD 31 of the plural IPDs 30 is connected to the
load L1 (hereinafter referred to as low-voltage drive load L1)
which is required to be driven when the voltage from the battery B
drops.
[0030] Each of the plural IPDs 30 has a GND terminal (ground
terminal) T.sub.GND being grounded. The IPD 31 connected to the
low-voltage drive load L1 is grounded via a diode D.
[0031] In this configuration, for example, if the ignition switch
is turned on, the control unit 20 receives the signal representing
this turning-on and starts its operation. Then the control unit
outputs ON signals to the IPDs 30 connected to the plural loads L
to be driven, respectively. Consequently these plural loads L are
supplied with power and driven.
[0032] However, during cranking or the like upon starting an engine
in which the voltage from the battery B drops temporarily, the IPD
30 operates its low-voltage shut-off function and is placed in an
off state. As a result, when the voltage from the battery B drops,
the low-voltage drive load L1 required to be driven is not
driven.
[0033] In view of this, the load drive circuit 1 according to the
embodiment is provided with a low-voltage detection circuit 40, a
negative-voltage generation circuit 50, an OR circuit 61, an AND
circuit 62, a ground-line change-over switch (switch unit) 70, a
voltage conversion circuit 80 and a connection line 11.
[0034] The low-voltage detection circuit 40 is a circuit for
detecting that the voltage applied from the battery B is a
low-voltage detection threshold value (predetermined value) or
less, and outputs a low-voltage detection signal S1 when the
applied voltage is the low-voltage detection threshold value or
less. The low-voltage detection signal S1 is applied to the OR
circuit 61.
[0035] The OR circuit 61 turns the ground-line change-over switch
(hereinafter simply referred to as switch) 70 on when a GND switch
ON signal (ground switch-on signal) S2 from the control unit 20 or
the low-voltage detection signal S1 is inputted. The GND switch ON
signal S2 is outputted in a time period such as the cranking time
where the voltage from the battery B is expected in advance to be
the low-voltage detection threshold value or less. The GND switch
ON signal S2 is continuously outputted during this time period.
[0036] The AND circuit 62 outputs a negative-voltage generation
signal S5 when both a signal S3 outputted upon turning-on of the
ignition switch and a signal S4 from the control unit 20 are
received. The signal S4 is outputted in an activation state of the
control unit 20.
[0037] The negative-voltage generation circuit 50 generates a
negative voltage (e.g., -2V) lower than a ground side voltage
(i.e., 0V) of the IPD 30. An output of the negative-voltage
generation circuit 50 is connected via the switch 70 to the GND
terminal T.sub.GND of the IPD 31 which is connected to the
low-voltage drive load L1.
[0038] Desirably none of the GND switch ON signal S2 and the signal
S4 is outputted during a timing where the driving of the
low-voltage drive load L1 is not necessary. This is because the
low-voltage shut-off function is not required to be avoided during
the timing where the low-voltage drive load L1 is not driven. The
timing where the driving of the low-voltage drive load L1 is not
necessary can be determined depending on whether or not a start
request signal for the low-voltage drive load L1 outputted from,
for example, a host device is inputted into the control unit 20.
Thus the negative-voltage generation circuit 50 generates the
negative voltage when the start request signal (signal representing
necessity of driving) for the low-voltage drive load L1 is
inputted, and inhibits the generation of the negative voltage when
the start request signal is not inputted.
[0039] FIG. 2 is a circuit diagram illustrating details of the
voltage conversion circuit 80 of the load drive circuit 1 according
to the embodiment. For convenience of explanation, FIG. 2 also
illustrates the control unit 20, the IPD 31, the negative-voltage
generation circuit 50, the connection line 11, etc.
[0040] As shown in FIG. 2, the voltage conversion circuit 80
includes resistors R1, R3 and an N-type switching element S. The
switching element S is, for example, a PNP transistor having a base
connected to the control unit 20 via the resistor R1, an emitter
connected to the power supply 10 and a collector connected to an IN
terminal (input terminal) T.sub.IN of the IPD 31 via a resistor R2.
The resistor R3 is connected between the collector and emitter of
the PNP transistor as the switching element S.
[0041] The connection line 11 connects between the IN terminal
T.sub.IN and the GND terminal T.sub.GND of the IPD 31. A resistor
R4 is provided on the connection line 11.
[0042] Next an operation of the load drive circuit 1 according to
the embodiment will be explained. FIG. 3 is a detailed circuit
diagram illustrating a main portion of the load drive circuit 1
according to the embodiment. As shown in FIG. 3, a limit resistor
R5 is provided on the way of a path from the OR circuit 61 to an
N-channel FET as the switch 70. A path 13 is branched from a
portion, between the OR circuit 61 and the limit resistor R5, on
the way of a path 12 from the OR circuit 61 to the switch 70, and
connected to the negative-voltage generation circuit 50. The
N-channel FET has a source connected to the negative-voltage
generation circuit 50 and a drain connected to the GND terminal
T.sub.GND.
[0043] In such the circuit configuration, the switch 70 is turned
off when none of the low-voltage detection signal S1 and the GND
switch ON signal S2 are inputted to the OR circuit 61. As a result,
the GND terminal T.sub.GND of the IPD 31 is grounded via the diode
D (see GND current path [normal time] shown by a broken arrow). In
contrast, the switch 70 is turned on when the low-voltage detection
signal S1 or the GND switch ON signal S2 is inputted to the OR
circuit 61. As a result, the GND terminal T.sub.GND of the IPD 31
is connected to the negative-voltage generation circuit 50 and
applied with the negative voltage (see GND current path
[voltage-drop time] shown by a solid arrow).
[0044] FIG. 4 is a timing chart illustrating an operation of the
load drive circuit 1 according to the embodiment. The timing chart
illustrated in FIG. 4 represents an operation not taking the GND
switch ON signal S2 into consideration.
[0045] As shown in FIG. 4, the voltage from the battery B is
supposed to be V1 at a time 0. The voltage of the GND terminal
T.sub.GND is 0V. Then the voltage from the battery B is supposed to
start reducing from V1 at a time t1 and reach the low-voltage
detection threshold value at a time t2. Thus the switch 70 is
turned on and the voltage of the GND terminal T.sub.GND becomes the
negative voltage generated by the negative-voltage generation
circuit 50. Next the voltage from the battery B becomes V2 at a
time t3.
[0046] A voltage value between the voltage V2 and the negative
voltage (see a range shown by an arrow in FIG. 5) is the operation
voltage or more of the IPD 31. Thus as the operation voltage of the
IPD 31 is secured, the low-voltage shut-off function does not
work.
[0047] Thereafter the voltage from the battery B keeps V2 and then
starts increasing at a time t4. Then when the voltage exceeds the
low-voltage detection threshold value at a time t5, the switch 70
is turned off and the voltage of the GND terminal T.sub.GND returns
to 0V. Then the voltage from the battery B reaches V3 at a time t6
and thereafter maintains V3.
[0048] Next an operation of the voltage conversion circuit 80 will
be explained with reference to FIG. 2. Firstly, in this embodiment,
in a case of turning the IPD 31 on, the control unit 20 outputs an
ON signal of an L level. Thus the switching element S is turned on
and the voltage of the power supply 10 is applied to the IN
terminal T.sub.IN. Further as the GND terminal T.sub.GND is
grounded and applied with 0V, the IPD 31 is turned on.
[0049] In contrast, in a case of turning the IPD 31 off, the
control unit 20 outputs an OFF signal of an H level. Thus the
switching element S is turned off. In this case, if the switch 70
is off, the IN terminal T.sub.IN is grounded via the connection
line 11 as well as the GND terminal T.sub.GND, whereby the IPD 31
is turned off. Even if the switch 70 is on, the negative voltage
from the negative-voltage generation circuit 50 is applied not only
to the GND terminal T.sub.GND but also to the IN terminal T.sub.IN
via the connection line 11. Thus the IPD 31 is turned off.
[0050] FIG. 5 is a circuit diagram illustrating a modified example
of the load drive circuit 1 according to the embodiment. In this
example, for example, the connection line 11 is removed from the
load drive circuit 1 shown in FIG. 2, and the control unit 20
outputs an ON signal of an H level in a case of turning the IPD 31
on and outputs an OFF signal of an L level in a case of turning the
IPD 31 off.
[0051] In this arrangement, in a case of turning the IPD 31 on, a
switching element S' as an NPN transistor is turned on in response
to the ON signal of the H level, the voltage from the power supply
10 is applied to the IN terminal T.sub.IN. Further as the GND
terminal T.sub.GND is grounded and applied with 0V, the IPD 31 is
turned on.
[0052] In contrast, in a case of turning the IPD 31 off, the
switching element S' is turned off in response to the OFF signal of
the L level. Thus the IN terminal T.sub.IN becomes at 0V. If the
switch 70 is off, as the GND terminal T.sub.GND is grounded and
applied with 0V, the IPD 31 is turned off. In contrast, if the
switch 70 is on, as the IN terminal T.sub.IN is at 0V and the GND
terminal T.sub.GND is at the negative voltage, the IPD 31 is
occasionally turned on. That is, the IPD 31 may be turned on
unintentionally.
[0053] In this respect, the voltage conversion circuit 80 shown in
FIG. 2 has a function of, in cooperation with the connection line
11, preventing the IPD 31 being turned on by the application of the
negative voltage to the GND terminal T.sub.GND from the
negative-voltage generation circuit 50 when the control unit 20
outputs the OFF signal with respect to the IPD 31.
[0054] The case where the IPD 31 is turned off corresponds to a
timing during which the driving of the low-voltage drive load L1
connected to the IPD 31 is not necessary. Thus, in this case, the
negative-voltage generation circuit 50 does not seem to generate
the negative voltage. However, supposing that the load drive
circuit 1 according to the embodiment performs a driving control
with respect to a plurality of the low-voltage drive loads L1, the
negative-voltage generation circuit 50 generates the negative
voltage when at least one of the plural low-voltage drive loads L1
is required to be driven. In other words, there is a case that the
IPD 31 corresponding to at least one of the plural low-voltage
drive loads L1 is turned on and the IPDs corresponding to the
remaining low-voltage drive loads L1 are turned off. In this case,
as the problem explained with reference to FIG. 5 may occur, the
circuit configuration shown in FIG. 2 is useful.
[0055] As described above, according to the load drive circuit 1 of
the embodiment, when the voltage from the battery B is detected to
be the low-voltage detection threshold value or less, as the switch
70 is turned on and connects between the negative-voltage
generation circuit 50 and the GND terminal T.sub.GND of the IPD 31,
a voltage of the GND terminal T.sub.GND of the IPD 31 becomes the
negative voltage generated from the negative-voltage generation
circuit 50. Thus as the GND terminal T.sub.GND is at the negative
voltage even when the voltage from the battery B drops, the
operation voltage of the IPD 31 can be secured and hence the
low-voltage shut-off function can be avoided. Further as the
low-voltage shut-off function can be avoided in the aforesaid
manner, it is not necessary to provide an auxiliary battery or a
power system not relating to the engine start, etc. or to mount a
DC/DC converter. Accordingly the load can be driven by avoiding the
low-voltage shut-off function during the voltage drop, while
suppressing the necessary number of large sized components without
requiring entire change of the power supply system.
[0056] Further the negative voltage is generated when the start
request signal for the low-voltage drive load L1 is inputted, and
the generation of the negative voltage is inhibited when this
signal is not inputted. Thus in a case where none of the
low-voltage drive loads L1 are required to be driven, as the
negative voltage is not generated, power consumption can be
suppressed.
[0057] Further, in the time period where the voltage from the
battery B is expected to drop, the GND switch ON signal S2 is
outputted, thereby causing the switch 70 to connect between the
negative-voltage generation circuit 50 and the GND terminal
T.sub.GND of the IPD 31. Thus, for example, in a case where the
voltage from the battery B is the low-voltage detection threshold
value or less, even if the switch 70 is not turned on in response
to the output from the low-voltage detection circuit 40 due to a
failure of the low-voltage detection circuit 40 or the like, the
ground side voltage becomes the negative voltage in the time period
where the voltage from the battery B is expected to be the
low-voltage detection threshold value or less. Consequently as the
operation voltage of the IPD 31 can be secured, the low-voltage
shut-off function can be avoided.
[0058] Furthermore, in order to prevent the IPD 31 being turned on
by the negative voltage applied to the GND terminal T.sub.GND of
the IPD 31 in the case of outputting the OFF signal with respect to
the IPD 31, the voltage conversion circuit 80 is provided.
Accordingly the IPD 31 can be prevented being erroneously turned on
due to a fact that, for example, the IN terminal T.sub.IN of the
IPD 31 is at 0V and the GND terminal T.sub.GND is at the negative
voltage.
[0059] As described above, although the present invention is
explained based on the embodiment, the present invention is not
limited to the embodiment but may be changed within a range not
departing from the gist of the present invention. For example, the
various kinds of resistors and the switching element S, etc. can be
suitably changed within the range not departing from the gist of
the present invention.
[0060] Further, although the IPD 30 is explained as an example of
the semiconductor relay, the semiconductor relay may be a device
formed by combining a predriver (having the low-voltage shut-off
function) and an MOSFET, for example, or another device.
[0061] Further, when a failure of the low-voltage detection circuit
40 or disconnection or the like of a path from the battery B to the
low-voltage detection circuit 40 occurs, the signal S4 may be
outputted just before or simultaneously with the GND switch ON
signal S2. When the failure of low-voltage detection circuit 40 or
the disconnection or the like of the path from the battery B to the
low-voltage detection circuit 40 occurs, the output of the OR
circuit 61 is substantially controlled only by the GND switch ON
signal S2 from the control unit 20. Thus, in correspondence to the
GND switch ON signal S2, the signal S4 may be outputted just before
or simultaneously with the GND switch ON signal S2. Of course, with
respect to such the failure or the disconnection, a circuit for
diagnosing the failure of low-voltage detection circuit 40 or a
circuit for detecting the disconnection of the path from the
battery B to the low-voltage detection circuit 40 is required.
[0062] Features of the load drive circuit according to the
embodiment of the present invention will be briefly summarized and
listed below in [1] to [4].
[0063] [1] A load drive circuit including a semiconductor relay
which is turned off when a predetermined operation voltage cannot
be secured, and which shuts off power supply to a load when the
semiconductor relay is off, the load drive circuit including:
[0064] a low-voltage detection circuit which detects that the
operation voltage is a predetermined value or less;
[0065] a negative-voltage generation circuit which generates a
negative voltage; and
[0066] a switch unit which is turned on and connects between the
negative-voltage generation circuit and a ground terminal of the
semiconductor relay, in a case where the low-voltage detection
circuit detects that the operation voltage is the predetermined
value or less.
[0067] [2] The load drive circuit described in [1], wherein the
negative-voltage generation circuit generates the negative voltage
in a case of receiving a signal representing necessity of driving a
low-voltage drive load, and inhibits generation of the negative
voltage in a case of not receiving the signal, the low-voltage
drive load being a load which is determined in advance to be driven
even in a case where the operation voltage drops and hence the
predetermined operation voltage for the semiconductor relay cannot
be secured.
[0068] [3] The load drive circuit described in [1] or [2], further
including a control unit which outputs a ground switch ON signal in
a time period where the operation voltage is expected to be the
predetermined value or less, wherein
[0069] the switch unit is turned on and connects between the
negative-voltage generation circuit and the ground terminal of the
semiconductor relay when the ground switch ON signal is outputted
from the control unit.
[0070] [4] The load drive circuit described in [1] or [2], further
including:
[0071] a control unit which outputs an ON/OFF signal for the
semiconductor relay;
[0072] an input terminal of the semiconductor relay to which a
signal according to the ON/OFF signal is inputted, and a connection
line which connects the ground terminal; and
[0073] a voltage conversion circuit which prevents, in a case where
the control unit outputs the OFF signal for the semiconductor
relay, the semiconductor relay being turned on by the negative
voltage applied to the ground terminal of the semiconductor relay
from the negative-voltage generation circuit.
[0074] A detailed description has been given of the present
invention referring to the specific embodiment, but it will be
clear by those skilled in the art that various changes and
modifications can be made without departing from the spirit and
scope of the present invention.
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